Treating clay for transportation and handling



Patented flan. 2, 193d new 1 NT OFFER panama CLAY FOR TRANSPORTATION AND HANDLING William S. Wilson, Boston, Mass., assignor to Merrimac Chemical Company, Inc., Boston, Mass., a corporation oi Massachusetts No Drawing; Application February 21, 1930 Serial No. 430,455

SCIaimS.

My invention concerns the treatment of clay for transportation and handling, and will be best understood from the following description of an example of the practice of the invention, the scope 5 of which latter will be more particularly pointed out in the appended claims.

Clay and clay minerals are used extensively in the arts, particularly in the paper and ceramic industries. Clay as mined contains a large percentage of water, and in shipping the clay to'reduce freight charges the material commonly is first dried, for example, by spreading the clay in a layer, say about 5 inches thick, over a floor which is heated. The final product is a mixture of powder and lumps of clay the latter, which are of irregular size, being commonly hard and tough and dimcult to disperse in water for use in the various arts.

The prior process has the objection that it is slow and that it produces a product which-is difficult, inconvenient, and expensive to handle. Usually all the moisture is not driven out of the clay by the drying process so as to reduce to some extent the dust nuisance in handling the mate- 5 rial.

2 According to the present invention the clay is formed into small sizes which are then dried without deorepitation to form relatively small, formretaining masses. It is possible by the improved process completely to dry the clay, with no nuisauce or loss from dust, and with a consequent reduction in the weight of the product and in freight charges for shipping it. Further, the improved material having in the mass a low angle of repose may be-handled in chutes and conveyers like wheat and other granular material much more readily than the material produced by the prior process because said latter material has a very high angle of repose. The improved material entirely eliminates the dust nuisance and is readily dispersible with water. this latter property enabling the material for example to be placed in a paper beater without first reducing it to a powder, and further greatly reducing the power consumption and time required for blunging the material to prepare it for use in the ceramic arts.

As an example of practising the invention, but

.without limitation thereto, wet clay may be extruded through dies to produce short cylinders, say about of an inch in diameter, the extruded clay it having been found breaking, due to handling and the drying, into slightly curved lengths from about to of an inch long. For this purpose the well known type of auger extrusion machine may be employed.

Preferably, the clay being extruded is caused to have a water content in the vicinity of the optimum water of plasticity, which content for average clays will be about 35% in respect to dry clay. This content, however, to secure best re sults in respect to retention of form and drying of the extruded clay bodies, must be varied for many clays. Commonly the water content will be between 30 and 40%. In some instances clays as mined may be directly extruded without prior washing, and in some instances without adjustment of the moisture content.

The extruded clay may be heated on a floor as hereinbefore referred to, the time necessary for drying the clay being much reduced as com- 7 pared to the prior process. Conveniently, how'- ever, the clay after extrusion is passed through an oven, say a rotary kiln of common construction, and heated therein for about 3 hours .at 100 13., or in less time by blowing hot air over it. The safe temperature and time for drying the clay will vary with the nature of the clay, the size of the forms, and the amount of moisture it contains. To prevent deorepitation 'of the forms, caused by driving off the moisture too rapidly, apparently the temperature must be decreased with the increase in moisture content and the distance from the center to the surface of the clay bodies. With many clays the temperature may be materially increased above that given above, as for example, with forms of the shape and size above given, Bennington, Vermont clay in the nature of kaolinite containing 36% moisture, and having the analysis listed below, has been dried without deorepitation of the forms by heating it for 4 minutes at 520 C.

SiO: (total) 48.90 A1203 (total) f 34.88 F9203 .80 T10, 1.15 CaO .30 M30 .8! K20 1.89 H20 lcombmed) 11.47 1 100.26 In general the selected heat treatment for drying the clay will, to a large extent, depend upon the" specific nature of the clay and the use to be made of the dried product, it being obvious that the temperatures and other factors should not be such as will destroy such properties of the clay as may de desirable in respect to the use to be made of the dried product. ForllO example, when the dried product is to be employed for use as a filler, the temperature should not exceed that which will destroy the property of ready dispersion in water. For average clays satisfactory results in respect to the economic production of a water dispersible product will be secured at temperatures of about 100 C. When the product is to be employed in the ceramic arts many clays may with advantage be dried at temperatures of from 200 to 300 C. to improve their working and dry "shrinkage properties. In all cases the drying may be accomplished more efliciently and uniformly than with the prior process due to the loose and uniform nature of the mass of extruded clay bodies.

The maximum temperature for drying the clay should not exceed that which will cause inciplent fusion or calcining of the clay, which will occur with the above mentioned clay if it is heated for about 1 hour at 650 C., or to a higher temperature, say at about 850 C. for 20 minutes.

It will be understood that the invention is not limited to any particular size and shape of clay bodies, or to the dimensions given in the above example of the invention. Spherical, spheroidal, ribbon, tubular, fluted, and small flat foraminous shapes, and the like, may be employed, but for practical purposes these are more expensive to produce and more diflioult satisfactorily to handle than cylindrical shapes. It will also be understood that the length of the shapes may.

be increased with their cross-sectional area without undue likelihood of the forms breaking during handling.

of so-called flint clays, as for example indianaite, may be broken into sizes and dried. For example, indianaite; which breaks with a conoidal fracture, may be broken in a machine similar to a coal breaker and screened to various sizes.

The screenings may be ground, for example in a ball mill, fine enough to pass through a 60 mesh screen and the ground product moistened and molded as above described. The broken sizes, say about the size of pea coal, and molded shapes may be dried as above described, and, if desired, the broken sizes and molded shapes may be mixed and treated together.

It will be understood that the above described examples of the practice of the process and of materials and apparatus are illustrative only, and that wide deviations ,may be made from them without departing from the spirit of the invention.

lclaim:

l. The process of treating clay for transportation which consists in forming it while wet into short cylindrical shapes and drying the latter without decrepitation thereafter transporting the clay in the dried condition and subsequently rendering the product plastic with the addition of water.

,crepitation thereafter transporting the clay in the dried condition and subsequently rendering the product plastic with the addition of water.

3. The art of handling clay for ceramic purposes and the like which comprises extruding the clay through an aperture while in a plastic condition to form elongated bodies of uniform crosssectional dimension, drying the extruded material whereby a material which may be handled readily is obtained, transporting the clay in this condition and subsequently dispersing the product with water preparatory for the manipulation of the clay in plastic form.

4. A method of handling clay for use in the ceramic and allied arts which comprises forming the clay into a plastic condition and extruding the same whereby elongated bodies of substantially uniform cross-section are produced, drying the extruded product'below a temperature which brings about decrepitation, transporting the product and subsequently rendering the product plastic and moldable by the addition of water thereto.

5 The method of handling clay. for use in the ceramic and alliedarts which comprises forming a clay while in a plastic condition into small shapes of substantially uniform cross-section, drying the same while avoiding decrepitation, transporting the clay in the dried condition and subsequently rendering the same plastic and moldable by the addition of water. i

WILLIAM S. WILSON. 3 

